Silicone resins which are a family of high molecular weight compounds are less expensive and easier to process than quartz glass. Like acrylic resins, epoxy resins and fluorinated polyimide resins, silicone resins are regarded useful as optical propagation media for optical waveguides or the like. By imparting photo-curability to these resins, pattern formation by photolithography becomes possible. Few materials which have high resolution in aqueous solution are available from silicone resins because of their characteristics. The use of alkali-soluble polysiloxane resins as resist material is described in JP-A 3-288857, JP-A 4-070662 and JP-A 4-338958 corresponding to U.S. Pat. No. 5,457,003, but none of them exhibit good patterning performance on alkali development as an optical waveguide-forming material.